The invention relates to image forming systems, and more particularly relates to modifying the arrangement of ejector sites in printheads disposed within the image forming systems to result in a printhead less susceptible to minor non-uniformities, and misalignments.
There are a number of different image forming technologies currently available for generating images on a print medium, such as a paper sheet. The electrostatic image forming system, being one type of image forming system, is generally known to those skilled in the art and is discussed herein as an exemplary image forming system. The electrostatic image forming system includes a printhead having a first electrode layer with a plurality of electrodes disposed on top of, and bonded with, a dielectric layer. The dielectric layer further couples to a second electrode layer. The second electrode layer also comprises a plurality of electrodes. One of the electrode layers most typically is a collection of RF-line electrodes, while the other of the electrode layers is most typically a collection of finger electrodes. The electrodes from the first electrode layer form intersections with the electrodes from the second electrode layer as viewed from a point in space generally orthogonal to the plane containing each of the electrode layers. However, the electrodes themselves are actually separated and electrically insulated from each other by at least one dielectric layer, or composition, as viewed from a cross sectional perspective of the printhead film containing the electrode and dielectric layers. The electrode intersections form charge generation sites, or ejectors, for emitting charges directed toward a dielectric image receiver in an image forming system. The final image forms by selectively toning the electrostatic latent image on the dielectric receiver and transferring the toned image to the print medium. The electrostatic image forming system is one example of an image forming system that can benefit from the teachings of the present invention.
Another exemplary type of image forming system is an acoustic ink printing system, is another one of the aforementioned types of image forming systems that can benefit from the teachings of the present invention. The acoustic ink printing system (AIP system) is an example of a system that employs focused acoustic energy to eject droplets of marking material, such as ink, from a printhead onto a printing medium. Printheads utilized in AIP systems most often include a plurality of droplet ejectors, each of which emits a converging acoustic beam into a pool of fluid, such as ink. The converging acoustic beam focuses at the interface between the ink and the air. The modulation of the radiation pressure exerted by the beam of each print ejector against the surface of the ink selectively ejects droplets of ink from the surface.
There is typically a collection, or grouping, of ejectors disposed on one or more printheads within the image forming systems described above, and in other image forming systems not specifically detailed herein. These ejectors can take the form of, e.g., charge generation sites, or ink ejectors.
AIP image forming systems typically utilize multiple rows of ejectors. A xe2x80x9crowxe2x80x9d of ejectors is the grouping of all ejectors within a printhead that lie on a straight line perpendicular to the printing direction. Generally each row (at least of a given ink color or ejectors) is offset in this perpendicular direction so that ejectors do not line up in the printing direction. They are typically equally spaced. For example, in the AIP system the rows are offset with a one pixel shift in each ejector row position relative to adjacent rows, to achieve full area coverage of a document when printing at 600 dpi resolution (see FIG. 4). If the AIP printhead is aligned and thus scans in a direction that is not perfectly perpendicular to the printing direction, then non-uniform gaps or overlaps can appear in the printouts at N-pixel intervals, where N is the number of rows of ejectors in the printhead. If all ejectors were in a single row then although the misalignment would have caused all printed image lines to be spaced with smaller gaps, these gaps would have been uniform and thus not objectionable. Anomalies in the addressing of the RF-drive signal used in powering the ink ejectors, or any other row to row ink pressure, flow, or dimensional non-uniformities in an AIP image forming system, can also allow spatial and electronic non-uniformity in the printhead to cause differences in the ink droplet volumes produced by ink ejectors in different rows of the printhead. The visual frequency response characteristics of the human eye is such that these periodic N-pixel interval defects, which often occur in the most sensitive portion of the eye frequency response region, can exacerbate these aforementioned effects, and result in perceptible defects in the resulting printed images.
One known approach that makes use of the visual frequency response characteristics of the human eye is a printhead having an interlacing of upper (1-4) and lower rows (5-8) in a counter-current flow printhead in order to push visual artifacts from thermal non-uniformity to a higher spatial frequency by interlacing the large drops produced in warm regions with the smaller drops from cold regions.
There exists in the art a need for an image forming system that contains one or more printheads having a modified ejector arrangement, which hinders the effects of any number of circumstances (e.g., temperature gradients, fluidic pressure drops, malaligned printheads and drive signal inconsistencies and defects, and manufacturing defects such as film thickness variations acoss the printhead). Additional defects not specifically mentioned that vary across the printhead can be responsible for such printing defects. The present invention is directed toward further solutions in this art.
An image forming system is provided having a printhead in accordance with one example embodiment of the present invention. The printhead includes a plurality of ejectors arranged in one or more sequenced groups. Each of the ejectors has a sequence number assigned thereto, ranging from a minimum value and incremented to a maximum value within each sequence group. The plurality of ejectors have an arrangement such that a difference between the sequence number assignment of any two adjacent ejectors is less than a difference between the maximum and minimum sequence number assignment values.
The phrase xe2x80x9csequence numberxe2x80x9d denotes a number assigned to each ejector in a group within a printhead. The ejectors are attributed to groups according to electrical connections (not shown), or addresses, and can be in any number of different combinations. Each sequential electrical connection, or address, to an ejector results in the ejector receiving the next xe2x80x9csequence numberxe2x80x9d. Each group begins with a first electrical connection going to a first ejector having the sequence number xe2x80x9c1xe2x80x9d. Then, for each electrically subsequent ejector in the group, the next sequential integer is assigned as that ejector""s sequence number. The sequence number relates to the address by which the ejectors are identified electrically. The system, for example, can instruct various combinations of ejectors to emit ink, or a charge depending on the type of system. These instructions are implemented based on the sequence numbers. The system, for example, can instruct the xe2x80x9c1xe2x80x9d, xe2x80x9c3xe2x80x9d, xe2x80x9c5xe2x80x9d, and xe2x80x9c7xe2x80x9d ejectors to emit ink at a predetermined time and location. Corresponding instructions issue in a like manner and in myriad of number variations. The example printhead detailed herein has eight ejectors in each group (and hence eight rows), thus the sequence numbers range from xe2x80x9c1xe2x80x9d to xe2x80x9c8xe2x80x9d, however, the number of ejectors in each group, and therefore the corresponding sequence numbers can vary with different printhead designs.
The printhead, according to one aspect of the present invention, includes an arrangement of ejectors derived from a one-cycle sine wave pattern. The ejectors can be ink ejectors, charge ejectors, or the like. Each sequenced group, according to one embodiment, contains eight separate ejectors. The rows are in sequences where the maximum difference between sequence number assignments of any two adjacent ejectors in sequence of the one or more sequenced groups is two in the 1-cycle sine wave pattern (see FIG. 8).
The printhead, according to still another aspect of the present invention, has a predetermined arrangement of ejectors derived from a xe2x80x9c3-cyclexe2x80x9d wave pattern. The ejectors can be ink ejectors, charge ejectors, or the like. Each of the sequenced groups, according to one embodiment, contains eight separate ejectors. The maximum difference between the sequence number assignments of any two adjacent ejectors in sequence of the one or more sequenced groups is five in the 3-cycle sine wave pattern arrangement. The periodicity of the sequence numbers is three minima/maxima per grouping rather than one.
The pattern utilized in deriving the particular arrangement of ejectors can vary. The number of ejectors, in addition, can also vary beyond the eight ejectors described above and illustrated further below.